Drawing lubricant



United States Patent 3,377,278 DRAWING LUBRICANT Sergio A. Ruzza, Warren, Mich assignor to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware No Drawing. Filed July 5, 1966, Ser. No. 563,640 9 Claims. (Cl. 252-23) ABSTRACT OF THE DISCLOSURE A water dispersible composition adapted to be applied to the surface of metal stock so as to provide an adherent protective film which serves as a lubricant when the metal stock is worked. The composition comprises a protective colloid, a fatty acid soap, a lubricant pigment and potassium-sodium tartrate which was found to be an excellent lubricant and pigment stabilizing compound.

This invention relates to drawing compounds useful as lubricants in metal forming processes. More particularly, this invention pertains to new coating compositions adapted to be dispersed in water and then applied to the surface of metal stock so as to provide, when dry, an adherent protective film which serves as a lubricant when the metal stock is worked under pressure.

The principal function of a drawing compound is to serve as a lubricant so as to prevent the metal being worked from sticking to the die or seizing the tool. It also assists the flow of metal thereby reducing scratching or rupture of the metal being worked and increases die and machine life by reducing friction and dissipating heat when present. In addition, metal manufacturers and fabricators are increasingly demanding a drawing compound which provides some degree of rustproofing. For example, much sheet metal stock is stored for a period prior to its use, and if not protected, must be cleaned prior to use. Naturally this is undesirable since it requires time and is costly. However, if the drawing compound is capable of protecting the metal, the stock can then be initially coated with the drawing compound and stored for subsequent processing thereby eliminating costly cleaning at the time of fabrication.

In order to meet such requirements and provide a lubricant having thermal stability and good lubricating qualities at high pressures and temperatures, recourse has been made to incorporating pigments into the drawing compound since pigments provide good oxidation protection and superior lubrication at high pressure. Unfortunately, this approach has met with only limited success due to the difficulty of keeping the pigment dispersed in the drawing compound. Thus, experience has shown that the pigment settles out when the drawing compound concentrate is diluted with oil or water so as to form a lubricant composition which can then be applied directly to the metal surface by brush, swab, pad, spraying, rolls or dipping. Accordingly, the lubricant dispersion which when freshly prepared is quite satisfactory, quickly becomes inadequate upon settling of the pigment. Such vacillation is obviously not compatible with commercial operation since it renders the degree of lubricant protection indeterminable. Moreover, while various additives have been proposed for stabilizing pigmented lubricants, they have been largely ineffective or too costly.

Accordingly, it is an object of this invention to provide a new pigmented, metal working lubricant.

A further object is to provide a pigmented metal working lubricant concentrate, particularly suitable for drawing and stamping operations, which remains homogeneous and stable when diluted with water.

3,377,278 Patented Apr. 9, 1968 under high pressures and stress as in deep drawing operations.

Other objects and advantages of this invention will hereinafter be disclosed and will be obvious to one skilled in the art.

In accordance with my invention, an improved metal working lubricant concentrate composition is provided which is based on my discovery that the compound potassium-sodium tartrate will stabilize and keep lubricant pigments uniformly distributed throughout lubricants of the soap and fat type. Thus, the new lubricant concentrate of this invention comprises a water soluble protective colloid, a water dispersible fatty acid soap, a lubricant pigment, and a stabilizing amount of potassium-sodium tartrate. The concentrate is slightly alkaline.

Lubricant concentrates of the above composition are readily dispersible in water so as to form uniform and stable dispersions having good viscosity and lubricating characteristics. These dispersions provide adherent films upon metal surfaces when employed in either concentrated or dilute form and it has been observed that metal surfaces coated with the lubricant dispersion are highly immune to oxidation. Furthermore, the pigment component ofthe dispersion does not separate upon standing and hence its lubricating capabilities do not deteriorate.

As stated above, the problem of drawing compound pigment separation is widely recognized and the seriousness of the problem is evidenced by the number of articles relating to additives or milling techniques for imparting stability to pigmented drawing compounds. Accordingly, it was totally unexpected to discover a compound which itself was an excellent lubricant and, at the some time, promoted pigment stability. Thus, the lubricant concentrate of this invention does not merely incorporate a new stabilizing additive. The combination pigment stabilizer and lubricant compound is, as set forth above, the alkali metal salt of tartaric acid, specifically the organic cornpound potassium-sodium tartrate, or as sometimes written sodium-potassium tartrate. This organic compound'is frequently referred to as Rochelle Salt and it has the formula KNaC H O .4H O. It is a readily commercially available material in either crystalline or powder form. It should be understood that the potassium-sodium tartrate compound used in this invention is sometimes identified as Seignette Salt of the formula KNaC H O .3H O. Accordingly, the term potassium-sodium tartrate as used in this invention is intended to include both of the above salts. The reason for its stabilizing eifect on lubricant pigments contained in soap or fatty based lubricants, as well as themechanisms involved therein, is not completely understood.

The amount of tartrate salt which is required to effect pigment stability is primarily a function of the particular lubricant pigment and the quantity thereof which is used in the composition. Generally, it has been found. that good results have been achieved when the weight ratio of tartrate salt to pigment is in the range of about 5/1 to 20/1. However, since potassium-sodium tartrate is itself a good lubricating agent, lubricant concentrates containing up to about weight percentof the tartrate, based on the total weight of the concentrate, are effective in furnishing good lubricant protection;

The water protective colloid component of this inven tion can be any of those colloids commonly used in the lubricant art. The term protective colloid is well understood term of art although occasionally other terms are used to describe protective colloids such as protective agent, stabilizing colloid, stabilizing agent and suspension agent." In general, protective colloids used in aqueous systems are identifiable by their physical colloidal behavior rather than their chemical nature, and they raise the viscosity of aqueous systems in which they are dispersed in disproportionately great amount relative to the quantity thereof which is dispersed in water. Protective colloids which can be used in this invention include bentonite clay, agar-agar, gum arabic, Irish moss, albumen, starches, gelatine, alginates, casein, and vegetable proteins including corn and soya protein. The most preferred protective colloids for use in the composition of the invention are the water dispersible modified celluloses such as methyl cellulose, water soluble ether cellulose, sodium carboxymethyl cellulose, ammonium carboxyethyl cellulose, calcium carboxypropyl cellulose, methylethyl cellulose, hydroxyethyl cellulose, potassium carboxyhexyl cellulose, sodium cellulose glycollate, and the carboxyalkyl celluloses wherein the alkyl group contains from about 1 to 3 carbon atoms such as carboxymethyl cellulose and carboxyethyl cellulose.

The protective colloid to be effective, should be present to an extent of at least about 0.3 weight percent and an increasing amount should be employed at higher dilution ratios. Generally, between about 0.3 to 5 weight percent, based on the weight of the undiluted concentrate, has given satisfactory results.

The compositions of this invention include a water dispersible soap which acts as an initial lubricant between the die and metal stock at the lower temperature ranges encountered in the metal working process. In addition, the soap serves as a vehicle by which the pigment component of the lubricant is distributed uniformly over the surface of the metal stock. Examples of a suitable soap for use in this invention are those prepared by reacting an alkaline earth or alkali metal hydroxide with fatty acids such as are derived from beef tallow and which comprise, in general, both saturated and unsaturated fatty acids of 12 carbon atoms or more. Soaps derived from synthetic and vegetable fatty acids can also be used. Specific examples of such acids which may be used to form a soap for use in this invention are stearic, oleic palmitic, lauric, margaric, elaidic, erucic, behenic, arachidic, tridecoic and brassidic. From the foregoing it is obvious that the invention is not restricted to any par ticular soap. In fact, depending on. the intended use of the drawing compound, the soap component of the drawing compound can be completely or partially substituted by a fatty oil such as lard oil, palm oil, etc.; fatty ester such as esters of fatty acids with glycerine, sorbitol, diethylene glycol; or partial fatty esters. The preferred material, however, for use in this invention is a fatty acid soap selected from the group of calcium, sodium or potassium laurate, calcium, sodium or potassium palmitate, calcium, sodium or potassium oleate and calcium, sodium or potassium stearate. The amount of fatty acid soap used is dependent on the particular pigment and concentration thereof which is employed in the concentrate. Generally, at least weight percent should be incorporated and an amount in the range of about 10 to 75 weight percent, based on the weight of the concentrate is satisfactory.

The pigment component employed in the lubricant of this invention is selected so as to provide lubrication at the higher temperatures encountered in the metal working operation. Thus, the fatty acid soap will provide initial low temperature lubrication and pigment selection depends on the severity of .metal working and temperature encountered therein. For example, a' light draw of about 10 to percent might indicate the use of a relatively low melting pigment such as barium carbonate (174 C.) while a more severe draw would require the use of a pigment such as titanium dioxide which melts at about 1560 C. Examples of pigments which can be used in 4 this invention are talc, graphite, lithopone, calcium carbonate, lead carbonate, barium carbonate, mica, zinc oxide, magnesium carbonate and titanium dioxide. Generally, any pigment used in the paint art can be employed in this invention. The preferred pigment, however, is graphite since it provides excellent lubrication throughout an extremely wide range of metal working conditions. Thus, graphite has provided excellent lubrication in extreme draws wherein the reduction has exceeded 50 percent. The pigment need not be of a particular particle size but should be in a physical condition that permits it to be easily dispersed. Thus, it should be less than about 200 mesh (U.S. Sieve series) and, generally 325 mesh or smaller. The amount of pigment needed in the lubricant composition is primarily a function of the severity of the metal working operation. In general a pigment concentration in the range of about 0.5 to 8 weight percent, based on the weight of the undiluted concentrate is satisfactory.

In carrying out draws where the percent reduction is greater than about 30 percent, the metal stock should be preferably first coated with iron or zinc phosphate and then with the lubricant composition of the invention. Any of the proprietary phosphate coating compositions can be used for this purpose and good results have been obtained when the surface of the stock to be worked contains a minimum of about 1 gram of coating per square foot of area. Although not essential, it is also beneficial to employ a phosphate coating in light draw or reduction operations. In this instance, a coating covering of about 0.1 to 0.8, gram per square foot may be quite adequate.

The lubricant concentrate composition of this invention is mixed with water and the resulting lubricant dispersion upon being heated to a temperature in the range of about F. to 205 F. can then be applied to the metal stock to beworked by way of the various techniques set forth above such as spraying, immersion, painting, etc. Preferably, the surface to be coated is dipped in the lubricant dispersion for a period in the range of about /2 to 5 minutes and the lubricant composition then allowed to dry thereby forming an adherent coating on the surface of the metal. The degree of metal working to be performed will largely determine the quantity of water which should be blended with the composition of this invention. Thus, a dilute dispersion representing a weight ratio of water to lubricant concentrate of about 16 to 1 might be more than adequate for a light reduction of 10 to 15 percent, while a dispersion made up in the ratio of about 4 parts by weight of water to each part by weight of concentrate would 'be desirable for a 50 percent reduction.

The following example is provided to illustrate this invention and should not be considered as a limitation thereof.

Example 1 A lubricantconcentrate was prepared having the following composition:

Component: Weight percent Rochelle salt (NaKC H 0 -4H O) 59.0 Sodium stearate 29.0 Calcium stearate 6.0 Carboxymethyl cellulose 2.5 Graphite 3.5

Each of the components was in powdered form of 200 mesh particle size or less and the composition was prepared by blending the components in a mechanical mixer. The components can be blended in any order or sequence and the lubricant concentrate thus prepared is a dry mixture which can be conveniently stored for months without special storage precautions.

A lubricating bath was prepared by adding the above concenrate to water in the ratio of one pound of concentrate to one gallon water which was heated to a temperature of about 195 F. After a brief period of stirring, steel stock corresponding to SAE 1036 was immersed in the heated bath for approximately two minutes. The steel stock had previously been phosphate coated by immersion for a period of 40 minutes in a phosphating bath which was at a temperature of 200 F. The phosphating bath was prepared from a mixture of zinc phosphate, phosphorous acid and nitrate accelerator and had the following characteristics:

Specific gravity 1.540-1550 Phosphate (P (min.) grams per liter 490 Zinc (min.) do 170 Nitrate (N0 (min.) do 96 After immersion in the lubricant bath, the steel stock was air dried and then cold extruded so as to form a transmission output shaft. The extrusion was carried out by means of a 175 ton horizontal hydraulic extrusion press and the steel stock underwent about a 48 percent reduction.

Examination of 100 output shafts formed by the foregoing process revealed that the lubricant composition of this invention had completely protected the metal. No surface defects, seizing or scoring marks were found on the metal parts. The lubricant film which remained on the metal surface at the completion of the extrusion process was easily removable via a cold water wash.

The lubricant composition of this invention also pro vides excellent corrosion protection as evidenced by the fact that steel coated with the composition had no rust spots after a 5 months storage period whereas similar steel coated with a conventional drawing compound was extensively rusted.

It will be apparent from the foregoing that the objects of this invention have been obtained. An inexpensive, pigmented drawing lubricant of remarkable stability has been provided based on the discovery of the lubricating and pigment stabilizing eifects of potassium-sodium tartrate.

What is claimed is:

1. A lubricant concentrate composition adapted to be dispersed in water thereby forming a coating bath, said concentrate composition comprising a water soluble protective colloid, a water dispersible fatty acid soap having at least about 12 carbon atoms, a lubricant pigment and potassium-sodium tartrate, said tartrate and pigment being present in amounts such that the potassium-sodium tartrate to lubricant pigment weight ratio is between about 5/1 and 20/1 and said concentrate containing at least about 10 weight percent of said soap, and at least about 0.5 weight percent of said pigment.

2. A lubricant concentrate composition as set forth in claim 1 wherein said lubricant pigment is selected from the group consisting of graphite, talc, lithopone, calcium carbonate, lead carbonate, barium carbonate, mica, zinc oxide, magnesium carbonate, and titanium dioxide.

3. A lubricant concentrate composition as set forth in claim 1 wherein said protective colloid is selected from the group consisting of bentonite, starches, and carboxyalkyl cellulose.

4. A lubricant concentrate composition as set forth in claim 1 wherein said fatty acid soap is selected from the group consisting of calcium, sodium and potassium laurate, -palmitate, -oleate and -stearate.

5. A lubricant concentrate composition as set forth in claim 1 wherein said pigment is graphite.

6. A lubricant concentrate composition as set forth in claim 5 which contains about 0.5 to 8 weight percent of graphite based on the total weight of the composition.

7. A lubricant concentrate composition as set forth in claim 6 wherein there is at least about 10 percent by weight of a soap selected from the group consisting of calcium sodium and potassium laurate, -palmitate, -oleate and -stearate.

8. A lubricant concentrate composition as set forth in claim 7 wherein there is at least about 0.3 weight percent of a protective colloid selected from the group consisting of bentonite, starches and carboxyalkyl cellulose.

9. A lubricant concentrate composition as set forth in claim 1 comprising from about 0.3 to 5 weight percent of carboxymethyl cellulose, about 10 to weight percent of said water dispersible fatty acid soap, about 0.5 to 8 weight percent of graphite, and potassium-sodium tartrate in an amount such that the weight ratio of said tartrate to said graphite is between about 5/1 and 20/1.

References Cited UNITED STATES PATENTS 1,379,722 5/1921 Richardson 14827 X 1,946,121 2/1934 Wood 25229 2,760,931 8/1956 Spring et al 25249.5 X 2,825,693 3/1958 Beaubien et al. 25249.3 X 2,940,930 6/1960 Pattenden et al. 25241 X 2,965,567 12/1960 Brennan et al 25222 X 3,023,163 2/1962 Fucinari et al. 252493 X DANIEL E. WYMAN, Primary Examiner. PATRICK P. GARVIN, Examiner. 

